This allows to detect -s (--silent) option without checking GNU Make
version.

As commit e36aaea28972 ("kbuild: Fix silent builds with make-4")
pointed out, GNU Make 4.x changed the way/order it presents the
command line options into MAKEFLAGS.

In Make 3.8x, 's' is always be the first in a group of short options.
The group could be prefixed with '-'.

In Make 4.x, 's' is always the last in a group of short options.

As commit e6ac89fabd03 ("kbuild: Correctly deal with make options
which contain an 's'") addressed, we also need to deal with long
options that end with 's', like --warn-undefined-variables.

Test cases:

[1] command line input:    make --silent
     -> MAKEFLAGS for Make 3.8x:    s
     -> MAKEFLAGS for Make 4.x :    s

[2] command line input:    make -srR
     -> MAKEFLAGS for Make 3.8x:    sRr
     -> MAKEFLAGS for Make 4.x :    rRs

[3] command line input:    make -s -rR --warn-undefined-variables
     -> MAKEFLAGS for Make 3.8x:    --warn-undefined-variables -sRr
     -> MAKEFLAGS for Make 4.x :    rRs --warn-undefined-variables

We can take care of them, by filtering out long options (--%),
then matching -s% s% %s patterns.

Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com>
---

Changes in v2:
  - Fix makefiles under tools as well

 Makefile                       | 9 +--------
 tools/build/Makefile.build     | 8 +-------
 tools/scripts/Makefile.include | 8 +-------
 3 files changed, 3 insertions(+), 22 deletions(-)

diff --git a/Makefile b/Makefile
index b1ee4a49efa2..d8b5c4230da0 100644
--- a/Makefile
+++ b/Makefile
@@ -84,17 +84,10 @@ endif
 # If the user is running make -s (silent mode), suppress echoing of
 # commands
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),) # make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(filter -s% s% %s,$(filter-out --%,$(MAKEFLAGS))),)
   quiet=silent_
   tools_silent=s
 endif
-else                                   # make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  quiet=silent_
-  tools_silent=-s
-endif
-endif
 
 export quiet Q KBUILD_VERBOSE
 
diff --git a/tools/build/Makefile.build b/tools/build/Makefile.build
index e279a71c650d..850fe9ce47d3 100644
--- a/tools/build/Makefile.build
+++ b/tools/build/Makefile.build
@@ -19,15 +19,9 @@ else
   Q=@
 endif
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),) # make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(filter -s% s% %s,$(filter-out --%,$(MAKEFLAGS))),)
   quiet=silent_
 endif
-else                                   # make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  quiet=silent_
-endif
-endif
 
 build-dir := $(srctree)/tools/build
 
diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
index fc74db62fef4..7fda39adf3cc 100644
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -58,15 +58,9 @@ else
 NO_SUBDIR = :
 endif
 
-ifneq ($(filter 4.%,$(MAKE_VERSION)),)  # make-4
-ifneq ($(filter %s ,$(firstword x$(MAKEFLAGS))),)
+ifneq ($(filter -s% s% %s,$(filter-out --%,$(MAKEFLAGS))),)
   silent=1
 endif
-else                                   # make-3.8x
-ifneq ($(filter s% -s%,$(MAKEFLAGS)),)
-  silent=1
-endif
-endif
 
 #
 # Define a callable command for descending to a new directory
-- 
2.7.4

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